Regarding a high-precision power supply having a small variation in output voltage, for example, a control IC for high-precision switching power supply has been commercialized, the control IC switching values of a variable resistor embedded in a power-supply control IC chip by using a VID (voltage ID) code of 5-bit or 6-bit, and being capable of setting an output voltage in increments of 25 mV.
In addition, Japanese Patent Application Laid-Open Publication No. 2007-022298 and Japanese Patent Application Laid-Open Publication No. 2003-299349 each disclose a power supply circuit in which a plurality of adjusting resistors are arranged in parallel on one side of two voltage dividing resistors connected in series and a switch is provided to each of the adjusting resistors in series, and the power supply circuit adjusts its output voltage by determining on/off of each switch by digital signals.